Search for the gamma-ray spectral lines with the DAMPE and the Fermi-LAT observations

Weakly interacting massive particles, as a major candidate of dark matter (DM), may directly annihilate or decay into high-energy photons, producing monochromatic spectral lines in the gamma-ray band. These spectral lines, if detected, are smoking-gun signatures for the existence of new physics. Using the 5 years of DAMPE and 13 years of Fermi-LAT data, we search for line-like signals in the energy range of 3 GeV to 1 TeV from the Galactic halo. Different regions of interest are considered to accommodate different DM density profiles. We do not find any significant line structure, and the previously reported line-like feature at ∼133 GeV is also not detected in our analysis. Adopting a local DM density of ρ_ local=0.4 GeV cm^-3, we derive 95 velocity-averaged cross-section of ⟨σ v⟩_γγ≲ 4 × 10^-28 cm^3 s^-1 and the decay lifetime of τ_γν≳ 5 × 10^29 s at 100 GeV, achieving the strongest constraints to date for the line energies of 6-660 GeV. The improvement stems from the longer Fermi-LAT data set used and the inclusion of DAMPE data in the analysis. The simultaneous use of two independent data sets could also reduce the systematic uncertainty of the search.